1. Field of the Invention
The present invention relates to an encoding apparatus and an encoding method and, in particular, to an encoding apparatus and an encoding method for shortening delay time in an encoding process.
2. Description of the Related Art
Joint Photographic Experts Group (JPEG) standardized by the Internal Standard Organization (ISO) is available as a typical image compression method. In accordance with the JPEG standard, discrete cosine transform (DCT) is used and, it is known that if a relatively high number of bits is assigned, good encoded and decoded images result.
Methods of segmenting an image into a plurality of bands using a filter bank including a high-pass filter and a low-pass filter and encoding the image on a per band basis have been currently actively studied. The wavelet transform encoding draws attention as a new technique superseding the DCT because the wavelet transform encoding is free from block noise at high compression rate characteristic of the DCT transform.
JPEG2000 standardized January 2001 adopts a combination of the wavelet transform and highly efficient entropy encoding (bit modeling by bit plane and arithmetic coding) and provides a marked improvement in encoding efficiency in comparison with JPEG.
In a wavelet transform process, such as the one disclosed in Japanese Unexamined Patent Application Publication No. 10-283342, image data is input and a horizontal filtering operation and a vertical filtering operation are performed on the input image data while the image data is stepwise segmented into a low-frequency component.
Image data is wavelet transformed into coefficient data (frequency component). The wavelet transformed coefficient data is inverse wavelet transformed into original image data. The inverse wavelet transform restores finally the original image by performing a synthesis filtering operation on a high-frequency component and a low-frequency component from a topmost segmentation level to the lowest segmentation level.
Such an encoding system using the wavelet transform and the inverse wavelet transform finds applications in an image data transmission system such as a video conference or a video gaming system. More specifically, the image data is wavelet transformed on a transmitter side, and resulting coefficient data is entropy encoded and then transmitted as encoded date to a receiver side. At the receiver side, the received encoded data is entropy decoded. The coefficient data is then inverse wavelet transformed into the original image data. Such a series of processes is widely known.